I'm still trying to wrap my head around time signatures, but I think I'm stuck on where these metrical accents come from. For example, in 4/4, we say the main beats are Strong-Weak-Less Strong-Weak.
What, exactly, is making beats 1 and 3 stronger? I understand that in rock songs and such, the drums can provide rhythmic support, but in general, is the composer doing something that makes us feel a strong beat, similar to how poets carefully choose words with stressed syllables in particular positions for different types of meter? (Are composers typically taught to do something to emphasize strong beats in a piece?) I've seen resources (e.g. Laitz's The Complete Musician) discuss agogic or dynamic accents, but those seem to be described as distinct from metrical accents, i.e., marked changes that go counter to listeners' expectations. I do, however, notice some of these at the beginning of some measures, like durational and harmonic changes, but this isn't something that happens with every piece or even every measure in a piece.
So is it something mostly psychological perceived by listeners due to certain expectations? If so, what would give rise to this perception? I'm trying to imagine a violin or piano just playing a simple melodic line—do we still necessarily perceive or feel a certain time signature or meter, absent non-metrical accents?