When doing anything in life, obstacles will arise, and things may be tougher than you expected. But it's not the obstacles that will stop you from achieving your goals, it's how to handle those obstacles that matter. Are you able to take challenges and grow stronger from them or will you give up because of it?
The same concept can be applied to environmentalism - you might not be able to keep your ecological footprint down completely, but that doesn't mean you shouldn't try to make an effort when you can. Living sustainably is a journey that involves making mistakes, learning, being creative and trying new things. It is supposed to be imperfect, that's how we learn to make better change.