Enough fuel remains in the lines to get airborne
Years ago, I had a Titan Tornado II and under the direction of someone whom I placed a lot of trust in his experience because of my ignorance of experimental aircraft at the time, I installed an electric fuel pump he provided and insisted I install. Unbeknownst to me at the time, the fuel pump was from a motor vehicle and was not "free flowing."
Long story short; for my first maiden voyage, I started the Rotax 912, tightened the sea tbelts, (which prevented me from reaching the panel) taxied to the runway, did my run-up, and took off. 200' above the ground the engine stopped. Subsequently, I successfully made an off field landing by threading the plane through a myriad of perk holes in a subdivision under construction.
In hindsight, if I would have turned the electric pump on, the engine wouldn't have starved for fuel for that flight. But that fuel pump could've surely posed a problem in the future.
My ground operations before launching was anywhere between 5-10 minutes so, like stated before, one would be amazed at how long an engine will run with no fuel being supplied from the tank(s).
RV-4 0320\D3G 160, Whirlwind 200GA 70".