"Start your day with a smile, and it will smile back."
Optimism is a key factor to success, while a pessimistic attitude won't get you anywhere. Approach things open-mindedly, motivatedly and optimisticly, and you'll be treated with that same positive approach in return!
Oh, I totally understand you there — my life isn't easy or non-stressful either. I think this quote doesn't say bad/sad things should be unjustifiedly regarded as good though; it just emphasizes on the need to keep a little, sometimes even just a tiny bit of optimism in your mind at all times. Because if you don't, you will fall deeper and deeper into a bottomless pit of negativity towards anything, and it will become very hard to enjoy the positive aspects life has to offer.