If you're trying something new and you aren't sure of yourself, I would say it's pretty common to have a look around, say "hey that guy seems to know what he's doing" and then just follow along. There's nothing wrong with this - it can be a good way to start yourself off. It's how many people learn and it's how many people teach.
Taking this back to Jiu-Jitsu: say someone in the gym has a really good open guard. Nobody can pass it and he sweeps or subs everyone like it was nothing. You look at him, say "that looks cool! I want to do that too!" and all you do from then on is drill your guard game.
A few months pass. Maybe you've become hot stuff on the mats. Maybe you haven't - maybe you just don't feel comfortable playing open guard. The problem with "monkey see, monkey do" starts when all you do is imitate others.
Just because "hey, that guy makes it work" doesn't mean everyone will have the same kind of success with it. There are tons of reasons for this - attributes (gogoplata from closed guard, what?) and mindsets ("I'll wait and see what he gives me" vs. "If I don't explode right now I'm going to lose") are great examples.
Not everyone is insanely flexible, even if half the guys you train with seem to have some kind of genetic mutation. Likewise, if you're naturally agressive, you may not be well suited to a "lay & pray" game.
By default, your coach deserves trust (without which, there's really no point to your even being in the class). But the coach really only shows you your options - and you do need to take responsibility for the choices you make in training.
A coach can be a great fighter with the best triangle game in the world. You may have short legs or bad knees that mean your triangles are horrid. There should not be an issue here unless all your coach makes you do are triangles. You can learn to make your triangle more efficient but if it's not clicking, it's not clicking.
The whole point is to play and explore, to see for yourself what works and what doesn't. Sometimes you just know right away you won't like certain positions or techniques, and sometimes it may take you months of experimentation before you find out.
Don't be afraid to take parts of other peoples' games and make them your own - equally, don't be afraid to go your own way and try to find something that is truly yours.