Pros:
- Level of responsibility and opportunity you can get at an early stage startup WAY outstrips what an established company can typically offer you, especially if you are early career. You might be able to get more money at FAANGM, but your career will not grow as fast.
- Because of the above you get to learn skills that generalize (eg. how to deliver value with a product, how to negotiate a partnership, how to make an impact on a P&L). I've seen many folks come in from Big Co. who only know things that are specific to that company. The reason for this is that Big Co. has already figured out how work needs to get done to achieve their business objectives, and everyone who works there gets handed that API. I've seen folks come out of large companies and realize that they hadn't learned fundamental skills around how to generate value. That they had mostly built experience in how to operate in the environment they were in, but didn't translate outside. In startups you have to learn to generate value or the company dies.
- You get to make an asymmetric bet. If you're early career your opportunity cost is low but your capture could be high if it works out.
- The experience of working on an early stage team really trying to DO something is unparalleled. You won't find anything like it at Big Co. (unless you're lucky enough to get involved in a new product launch, which does happen).

Cons:
- You only get one bet at a time. This is as opposed to investors who get a portfolio. But your stake is usually smaller than theirs. So it's REALLY hard to hedge your risk. This is not a worry in your early career, since your alternatives are not great. But it becomes a problem later on. If you don't have personal liquidity, you really can't afford this by your mid-thirties.
- Returns are really skewed right now towards founders and investors (who dominate the cap table), and then the first "adult" executives brought in (who may not get the largest equity stakes but tend to be bonused out in cash even in the case of a fire sale, when most employees get nothing). IMO this is why startup recruiting is so hard right now. It's clear to anyone looking closely that the returns are so heavily founder/investor skewed that it makes no sense to join a company at an early stage if you have any other options.

IMO the biggest problem to fix is the lopsided cap tables. Without this it's really hard to attract talent. For most people who are startup focused, the competition is not a high paying job at FAANGM, but them starting their own thing. Here's a possible solution: Companies could start at their inception with 3 classes of shares instead of 2- preferred (for investors), 10x voting common (for founders), and 1x voting common (for employees). You could then allocate a MUCH flatter cap table so that you can make meaningful equity offers to attract folks to the early team who would otherwise have chosen to found a company themselves, but you don't run into the control issues you would otherwise run into due to diluting the founders stakes. There are certainly other solutions, but solving this problem is what I would advocate for- ie. make it more rational for someone to choose to work for your company as opposed to starting their own.