@Jason - Did you get out on the wrong side of bed this morning?
@horsewoman - Suppose I that I had just bought a horse for $200 on eBay and now asked a horse forum if it is was wrong to buy a horse since I don't know anything about horses, or if I bought the wrong horse, or maybe one that was too cheap? How is that question best answered? I don't know, because it's hard to know where to start answering and so forum answers to such questions have a way of turning into autobiographical opinions

But in general ... investing is unique because it contains both intellectual and emotional components. Therefore answers are rather individual although whenever it comes to individuals, we also know that many individuals are rather similar, especially at the early stages.
For example, right now the standard recommendation is something like 100% VTSAX or some balanced combination which satisfies both components. It is intellectually simple to understand. People can reference popularized accounts that are easy to read---JL Collins blog stock series which later turned into a best-selling book is immensely popular and a good starting point---and if they want to dive deeper they can find some old academic work that supports the strategy(*). It's emotionally satisfying because a) it is simple to understand; b) we're currently sitting on top of a bull market at several time-scales, particularly at the 10-year and 40-year scales, so you basically have confirmations from two (2!) generations; and c) there's the very important factor of social proof in that everybody else is doing it. Combining both, it's not only simple, it is also easy---both intellectually and emotionally.
(*) Even better! Newer work that goes against the thesis is mathematically complicated or requires a lot of effort to understand.
This is therefore where many people begin and end. But you bought a [random?] ETF, so now you gave up on the social proof aspect (although you're kind seeking it here with this question?

). From this follows the need to learn how to deal with things when your portfolio goes down/when it goes up but not as much as the market/when it goes up more than the market (was it skill or luck?). It's best to learn these emotional lessons with small amounts. Hence, it's good to have some skin in the game ... but not too much... even when improving on the intellectual side.
The intellectual side is as wide as it is potentially deep. Personally, I prefer to learn from textbooks rather than novels because the material is organized and you know you're not reading someone's autobiography. I've posted a link about my startup curriculum several times. This is more studying than most people are willing to engage in. However, for an overview, I recommend
https://www.amazon.com/dp/1580622011/ ... it's a bit dated in its assumptions (so don't copy it naively... "naive copy"-temperaments should stick to level 1 described above) ... However, it goes through essentially what it takes for the easy-road and the hard-road respectively for each investment types. It contains far more wisdom than what you see in most/modern "how to start investing"-type books.