Ask a losing trader about entries and they will talk for an hour. Ask them about position sizing and you get silence. Sizing is the part of the system that decides whether a losing streak is an inconvenience or an account reset.
The formula I use
I risk a fixed fraction of the account per idea, defined by the distance to invalidation, never by conviction. Conviction is a feeling; invalidation is a price. When the two disagree, the chart wins. That one rule has saved me more money than any indicator I have ever used.