Most of your suggestions are on point. This, however, is one that requires a bit more nuance.

As you say elsewhere, you should not invest money that you expect to need in the next few years. In that sense, if you may need it in the next few years, you can't afford to lose it, so don't invest it.

However, especially as your portfolio (hopefully) grows over time, your ability to replace it shrinks more and more (since you have less time until retirement and the amounts involved should be a large multiple of your annual income).

If one was to take your advice here at face value, they should take out of their investments any money that they can no longer reasonably expect to be able to replace. However, that severely limits their overall return and thus diminishes their retirement lifestyle.

This is why I'd modify your statement to "Never invest more than you can afford to lose in especially volatile and risky assets (think crypto). When you're investing in a prudent mix of stocks, bonds, cash-equivalents, real estate, etc., you can invest far more than you can afford to lose, since it's very unlikely that you'll lose it all.