What test is Fischer referring to when describing 1.e4 as "best by test"?

Question

Famously, Bobby Fischer describes the first move 1. e4 as "best by test". However,

Bobby Fischer exclusively opened his games with 1.e4...
_{“Best by test: 1.e4” (Bobby Fischer)}

Actually, Fischer didn't play 1.e4 100% exclusively, but it's very close. So it seems like Bobby Fischer didn't actually test non-e4 openings during tournaments all that much. As black, he scored better against 1.e4 than almost any other opening.

Hence the question:

Question: What test is Fischer referring to when describing 1.e4 as "best by test"?

Answer 1

The statement means that "tests" (games played) had shown, to Fischer's satisfaction anyway, that e4 is a better opening move than any other option.

His experience with the body of evidence available at that time (both his own games and the many games he studied) made his conclusion more than just a "best guess". It could be compared to the scientific method of hypothesis, test, repeat; where in this case the repeated tests (involving a variety of opening moves) showed (in Fischer's estimation) that e4 was the best opening move.

Modern speakers would likely include "statistically" in the statement for clarity (assuming it were true now like it was then): "e4 is the best, statistically". But that lacks the rhetoric punch of "best by test".

See also this chess.com article on the "Best by Test" statement , which assumes this meaning for Fischer's usage:

While there is no question much of chess is a matter of choice, what if you could know with mathematical certainty which is stronger: 1.e4 or 1.d4? The late Bobby Fischer swore by 1.e4, claiming it was "best by test", but that was before the era of databases.

Answer 2

"Best by test" simply means he derived his conclusion from experience - trial and error.

Answer 3

He meant in his opinion, it's more difficult to equalize as Black against 1.e4 than against other openings. By the quote alone it's not clear to see if he meant from a theoretical perspective (i.e: attempts through analysis) or from a practical one (i.e: attempts in real games on the board)

The scores of one individual player don't mean much, specially if we consider that Fischer was an extremely dynamic player who would perform best in positions arising from 1.e4.

Keep in mind that the statement was posed as a personal opinion (even though it's an expert one), not as the conclusion of any sort of research project. Multiple interpretations are possible and there may be evidence that prove some of them wrong