Running three ventures in overlapping windows taught me that conviction is cheap and timing is expensive. The idea quality across all three was similar; the outcomes diverged based on market timing and execution speed.
The hardest discipline is knowing which venture to protect and which to let go. Founders who cannot kill their own projects end up being killed by the market instead — slowly, and more expensively.
My current rule: every project gets a falsifiable thesis and a review date. If the thesis breaks, the project ends the same week — not the same quarter.