Pretty much sums it up.
Abu Sa’eed Al-Khudri reported: The Messenger of Allah, peace and blessings be upon him, said, “Let not one of you belittle himself.” They said, “O Messenger of Allah, how does one belittle himself?” The Prophet said, “He finds a matter regarding Allah about which he should speak up but he does not. Allah the Exalted will say to him on the Day of Resurrection: What prevented you from speaking up about such a matter? He will say: It was out of fear of the people. Allah will say: Rather, it is I who deserved to be feared.” [Ibn Majah]