How to Disagree Honestly and Get Away with It
Disagreement is a great opportunity to make a good decision, but it should be handled delicately. Hopefully you feel that you have expressed your thoughts adequately and been heard before the decision is made. In that case there is nothing more to say, and you should decide whether you will stand behind the decision even though you disagree with it. If you can support this decision even though you disagree, say so. This shows how valuable you are because you are independent and are not a yes-man, but respectful of the decision and a team player.
Sometimes a decision that you disagree with will be made when the decision makers did not have the full benefit of your opinion. You should then evaluate whether to raise the issue on the basis of the benefit to the company or tribe. If it is a small mistake in your opinion, it may not be worth reconsidering. If it is a large mistake in your opinion, then of course you must present an argument.
Usually, this is not a problem. In some stressful circumstances and with some personality types this can lead to things being taken personally. For instance, some very good programmers lack the confidence needed to challenge a decision even when they have good reason to believe it is wrong. In the worst of circumstances the decision maker is insecure and takes it as a personal challenge to their authority. It is best to remember that in such circumstances people react with the reptilian part of their brains. You should present your argument in private, and try to show how new knowledge changes the basis on which the decision was made.
Whether the decision is reversed or not, you must remember that you will never be able to say ‘I told you so!’ since the alternate decision was fully explored.