For me ive always felt ive been feed a bunch of bull shizen ; starting with santa claus but who knows maybe that guys real now; im a women so i go with my gut; i know when my boyfriends cheating kind of thing; the math hard evidence part ill leave for later; meaning my gut informs me then ill chk ure phone, hire the detective, gps ure car. So for me after exploring all the conspiracies out there; this one was the holy grail. I guess its more a question of what made u think that the shape of the earth was different from what uve been told and what r the implications of such a reversal.
The rectilineator experiment coupled with obvious space agency bullshit. Bendy light also helps.
Then there is other evidence which narrows the possibilities down such as the horizon line and distance and ships reappearing on the horizon after zooming in etc. When looking at the two remaining possibilities - flat or concave earth, flat also has impossibilities. This leaves concave Earth.