Easier said than done

You're not in very good shape. Your friend is giving you some advice. She says that you should exercise every day, but you're very busy so it's not easy to find time to exercise. You think in response to your friend's suggestion. 
Easier said than done.

(something is) easier said than done 

Use this expression when someone talks about something and makes it sound easy, but you think it's difficult.

For example, if your business is losing money and a friend says: Why don't you do some advertising and get some more customers?

You know that getting new customers is really difficult, so you might say or think:     Ha! That's easier said than done.

You can use this phrase in a variety of situations, from casual to formal.