Sizing one trade well is not enough. You also have to manage the whole account, because your real risk is all your positions added together, not any single one on its own.
If ten different coins all feel like the trade of the year and you go heavy on each, you are really making one giant bet. In a sharp selloff they tend to fall together, and that shared risk can wipe out far more than you planned to lose on any one.
Two simple habits keep this in check. First, cap how much of your account sits in the market at once, so you always hold cash for a clear head and better prices. Second, do not let one position grow so large that its blow-up alone would be a disaster.
Manage total exposure, not just single trades. No one position, and no one bad day, should ever be able to take down your account.
Tip. Coins that move together do not give you real diversification. Ten memecoins are closer to one big bet than to ten independent ones, so size the group, not just each name.