How do you decide your maximum risk per idea before you look at the chart?

Before a setup catches your eye, it helps to have a fixed number in mind for how much you are willing to lose if that idea is wrong. Many traders express this as a percentage of account equity, but the more useful step is working backward from the invalidation point: the price level where the thesis no longer holds. The distance from entry to invalidation, multiplied by the position size, gives the loss you would accept, and that loss should be set before the trade rather than adjusted to fit the chart you like. A common mistake is choosing size first and then placing the stop wherever it feels comfortable. That reverses the logic. The stop is determined by market structure and the reason for the trade, and size is then derived from the stop and your risk limit. If the derived size looks too small to be worth the effort, that is information too, and it may mean the setup is not suited to your account. I would be curious how others here handle the case where two ideas share the same driver. Do you count them against one shared risk budget, or give each its own?