I use a pretty simple test for determining whether it's a good idea for me to try stock picking: I go and take a look at the times for the men's 5,000 metres at the last Olympics.
Wait, bear with me.
In the market, the vast majority of actively traded money and stocks is in the control of professional money managers of one stripe or another. They're generally extremely intelligent, work incredibly hard, and are backed up by some of the most advanced analytical tools money can buy. And, generally speaking, they don't successfully outperform index funds.
If I decide that I can actively trade in this world and do better than the weighted average of this market, then I'm also implicitly deciding that my estimation of likely market moves is superior to that of some of the smartest, hardest-working people in the world. As mrspendy puts it, stock picking is an arrogant act.
This is why I look at the 5,000 metres. Thanks to the sheer weight of the biggest and most professionalised players in the market, trading in the stock market is roughly equivalent to running a 5k against Olympian specialists. Successfully competing at that level involves being the trading equivalent of an Olympic finalist. I know what my best 5k time is, and I can compare it to the last-placed finalist from Rio.
It turns out that Joshua Cheptegei ran that final in 13:09. My personal best is a solid eight minutes slower than that. Not only can I not run that kind of pace, I'd be out of my goddamned mind to imagine I could ever run that kind of pace. I am not lean enough. I am not long-legged enough. I do not cool fast enough. I do not train enough. I will never train enough. But if running was like investing, I could beat Cheptegei and claim a time of 13:06 and change, simply by indexing my run. No 5am alarms for double sessions, no vomiting on the side of the track after one sprint too many, no skipping roast potatoes at Christmas because it doesn't match my diet. Instead I just sign a piece of paper that says I understand I'll get the average time from the final, and I magically lose thirty kilos and gain fifty watts on my power threshold.
In other words:
1. The existence of the index fund is like being able to become a sub-14-minute 5k runner by signing a document.
2. Given that there are no medals for being best at retiring, refusing to sign that document because you think you can train hard enough to go to 13:03 is not a particularly sane option for people simply aiming to retire early.