It can be easy to be discouraged and think, "I'm not meditating enough" or long-enough but even Buddha got discouraged. He studied with several mystics before his enlightenment but was eventually discouraged by their teachings, which he felt unsatisfied with. In addition, he pursued extreme aestheticism only to be discouraged by it. During his meditation under the Bodhi tree, before his enlightenment, he was tempted by desires to abandon his practice. He could have easily given up after all of these events but he pressed on not knowing what would come next until he shattered the hold of the ego and realized enlightenment.
Something else to consider is that our sense of progress is too often seen through the eyes of the mind, which demands immediate, Earth-shattering and over-whelming results. So it can be hard sometimes to see our progress; especially since progress seems to unfold in increments. Yet even the lotus seed has to burst up through seemingly unending layers of mud and inches of murky, shifting water to eventually reach the top of the water to bloom in the sun. Our journey is similar. It seems like an impossible journey yet it has to be such for if the lotus grew instantly to the surface the stem wouldn't be strong enough to hold the enlightened flower.
So, we too must build a strong base or foundation for our practice. Thus, we don't need to worry so much about how "fast" we're growing in our practice. We can only grow as fast as our karma will allow. There is a lesson in everything and just because someone might seem "advanced" on the path doesn't mean they aren't having difficulties on their way to the sun too!! The goal isn't to keep up with some Zen master or those around you whom you consider stronger meditators but rather that we keep growing--period. I realized that wanting to be further along in my practice is giving into the desire for being better than others. It's hard to accept it but that's at the root because why would we be unhappy with our practice if we weren't trying to, not only keep up with others, but outdo them? As if it's a race to see who realizes enlightenment first. No, it's better for me to stay happy with where I am because like it or not, that is the only true reality. The rest is destructive delusion.