Mehdi Ghapanvari wants us to think of the poor, downtrodden non-clustered indexes:
Do you wonder why SQL Server ignores an index? Do you think about how you can deal with this problem? When you include too many columns in a query you decrease index selectivity. So, if you write a query like “Select * From …” the chance of choosing your nonclustered index will decrease.
The article is generally sound, though not all-inclusive. If you really want to use an index, you can use index hints. I personally have no qualms about using them, though hints are telling the optimizer that you know better than it, so be really sure you do actually know better than it before shipping that off.