Flatterers are the worst kind of enemies.

An enemy tells you where you stand; a flatterer removes your ability to know. The steady supply of agreement leaves you working from a picture of yourself that has been quietly edited, so you take wrong risks and misjudge how you are received. The damage is worse than opposition because you cooperate with it and feel good throughout.

Work out who around you has never once disagreed with you, and treat that as the warning it is. Then ask someone with nothing to gain from you what they honestly think of what you are doing. Make it easy for them to be blunt and do not argue with the answer.