A pitch that works has four parts: the specific problem, who it affects, what you propose, and why it is worth doing now. Lead with the problem, not your background. Keep it under two minutes. End on a concrete ask rather than trailing off, and expect the first question to be the one you skipped.
Under two minutes spoken, or four sentences written. The constraint is not about attention spans — it is a test of whether you have identified the essential part of your own idea.
A one-line story that IS the problem works well. A story that takes thirty seconds to arrive at the problem does not, because the listener spends that time trying to work out where you are going.
Say you do not know, then say what would tell you. "I do not know, and the way to find out is to try it with ten people first" is a stronger answer than a guess delivered confidently.