If someone says, "The best advice is found on the pillow," he/she means that it might not be good to worry about your problem now. You may be able to solve the problem after a good night's sleep. People often say "I'll sleep on it" to express the same idea.

eg: I don't think we can come up with any more answers tonight because we're all tired. Let's sleep on it. The best advice is found on the pillow.

Note:

The best advice is found on the pillow的意思是你最好先别担心，睡一觉也许明天一切就会好了。

例：我们都太累了，今晚也无法思考更多了。先睡一觉，明天再说。