When a user calls in for support they are already putting themselves at risk. There is not need for a support person to reinforce these feelings of inadequacy. No one gains from that type of power play. It is important to assure that user that this problem has happened to others before and will probably happen to others in the future. Clearly and quietly walk the user through the solution and insure that they understand how to solve the problem, should it occur again.
Support requires patience and understanding.
Making a user feel stupid will only assure an even great estrangement between users and support staff. Never demean the user. This might seem obvious but I have seen many support people who treat users as if they are bothering them. Simple user questions should be given as much attention, time and care and the more difficult ones. If support people are reaching the point of burnout and cannot give the user the attention they need and deserve, they should quickly be shuttled to another role in the department where they have less direct contact with users.