We've all been in class and seen that one person who just folds right over into a pose. And you are just sitting there thinking "Oh my God! How the hell do they do that?!" Then you look at your knees and think, "Why are you so damn far away?!??" Well mistake number one, we shouldn't be looking around class judging others or ourselves. But we all slip up now and then, we sneak a peak and get frustrated with ourselves. Instead of getting frustrated with yourself or jealous of that person, turn it into something like, "Wow they must've been practicing for years to get where they are at, I know I'll get there one day." More positive thinking, soon you'll realize your knees aren't that far away from your face and you'll be resting easily in that pose.
Balancing it out
Now here's where the balance comes in... sometimes with those super flexibility people they need to take a step back and strengthen other areas. I am guilty of this in one particular area of my body... my back. My thoracic spine likes to jut out, turn and do whatever the hell it feels like. So some back bends come very easily to me. It takes a lot of strength, control and focus to make sure my back doesn't arch in simple poses like Trikonasana (triangle). Pretty much I'm working my core tremendously to counteract what my body wants to do naturally.
That goes for people who can just drop down into those forward folds, take a step back, firm the proper muscles and work from there. It takes time and patience with yourself. You need to build up that strength to hold you up in arm balances, inversions or even your basic standing poses.
Yoga is the practice of tolerating consequences of being yourself