It's easy to maintain your goal weight if you truly enjoy the lifestyle you've created. Obviously, if you get up one day and say, 'Well I don't actually like going to the gym / tracking calories / etc., so I'll skip today', you've started to gain the weight already. The trick is finding a healthy lifestyle activity that can keep you active and that you can stick with. Climbing, running, hiking, kayaking / canoeing, cycling, tennis, etc etc are all great options if going to the gym to lift weights isn't your thing.