Don't ever say "Never"
Trading is a losing game. You sell because you need liquidity to by things you need. You sell because you wish to re-balance your portfolio. You don't sell "to rebuy lower".
Please do not say this as a global assertion just because it applies to you personally and to inexperienced traders. There are actually people who are very effective at trading. Not trading may be what is right..
for you, but not for everyone.