A misconception about blogging is that one needs X number of readers before it's worthwhile, where X is some dauntingly high number. But actually, you only need Y readers, such that when you write something good, there is a non-trivial probability that it will get shared to X number of readers. You don't need assurance that all of your good pieces will reach X number of readers; a glimmer of reasonable possibility is more than enough to motivate your gameplay. Cue that study about mice working more for probabilistic rewards than certain rewards. Thus, blogging becomes worthwhile dramatically sooner than the popular misconception has it.
I never expected to write so much, but I discovered that once I had a hammer, nails were everywhere, and that supply creates its own demand. I believe that someone who has been well-educated will think of something worth writing at least once a week; to a surprising extent, this has been true.Gwern
It is difficult for me to estimate values for X and Y, as these values are contingent on your aspirations and areas of interest. But I can certainly say that for me, the threshold where regular blogging became naturally self-motivating, when it turned from an aspiration and exercise in discipline to an active appetite, came sooner than I was planning for.
How many people do you need in your "audience" for your writing effort to feel worthwhile? I have high intrinsic motivation, so I think for me that number has always been relatively low. If yours is higher, then adjust my calculations accordingly. Three years ago, I might have thought the following (of course, these figures change over time due to hedonic adaption, etc.). I always expect most people to skip my weirdest or worst stuff, but if I could know that about 100 people would read all my best pieces, that would have been enough to keep me pumped for quite a while. I mean, aspiring writers before the internet had to write for a very long time with virtually no readers before they had any chance of gaining even 100 readers, so even just 100 readers should really feel like an extraordinary privilege and motivation.
Now, if you start with zero readers, let's say a brand new blog and you don't know anybody. A desired audience of 100 readers might seem unattainable, but remember, you don't need 100 people to know and like and read all your blog posts. All you need is a non-trivial probability of winning 100 readers in order for this desired audience to trigger effective motivation. So how do we estimate Y, the number of guaranteed readers you need to have a non-trivial probability of winning 100 readers total? And how do we define the non-trivial probability? Well, it will depend on the influence of the Y readers. A small number of people who can get it out to a large number of others, or a larger number of less influential people who will get it out to the same number of others. It will also depend on your personality characteristics, such as intrinsic vs. extrinsic motivation.
Let's say you can find only 10 people of the 7.5 billion people in the world, who will at least take a quick look at whatever you write. Virtually anyone can get this from some forum on the internet, like a subreddit related to the themes of your writing. A very quick Google says that the average Twitter user has 200 followers. Accounting for Twitter's unpredictable algorithm, let's say a random retweet from a random person is worth 5 views of your post. Pulling this out of my ass, but trying to be conservative. Let's assume you write something really good, which we'll define as being irresistibly compelling to the few people in your initial targeted audience base. Still, some will be too busy or distracted to share it, so even if it's irresistible, let's say only 20% of them share it with someone via Twitter. What this means is that when you write something good, it will very likely be read by at least 20 people (the first 10, then 2*5, so 10+10=20). Now, 20 people is not yet close to your desired 100, but the insight is that you're already 20% of the way to your goal and you literally just started from nothing. Now factor in the tail chance that one of those tweets gets retweeted by someone influential, and it's perfectly possible your post might randomly hit your 100-reader goal right out of the gate. But that's still rare at this point, this isn't quite yet a non-trivial probability of getting 100 readers. Yet, you can already see it on the horizon of attainability. If you are blessed with high intrinsic motivation, even this small glimmer of external hope might be enough to keep you churning.
Aside: Having analytics on your site really helps with the gamification. I suppose at some margins it could be perverse or destructive to get overly obsessed with the traffic data, but starting out I think it's hedonically productive on net.
If you have less intrinsic motivation and you need better chances than this to consider blogging a worthwhile venture, you could try to increase the initial number of people you give your work to. Or you could try to impress one person who is a little more influential. You could increase your volume. You can pursue any number of specific methods, suited to the strengths of your temperament, and avoiding the weaknesses of your temperament, to raise these numbers.
And of course, we're talking only about your genuinely good posts. Some, and perhaps many of your posts will go nowhere, but that's normal.
If your response to my perspective here is that it's hard to come up with so many ideas for posts, or that you're not getting even these small numbers of readers for your best posts, then maybe you just don't have that much to say, or you have nothing of value to offer anyone. Even still you're not yet hopeless: you could still try increasing your intrinsic motivation, and put all your eggs in the basket of enjoying the process and not caring what people think. Some figures have turned this into a very high art form, winning many readers in the long run. If you can't do that and you need external validation to keep writing, and you can't win for yourself these minimal quantities of nearly guaranteed external validation, then you're not a writer. You're a needy dumbass. You might still be qualified for a career in journalism.
But if you have even a few things to say, blogging is probably more worthwhile than you think.