'It's not your fault.'
'Everything happens for a reason.'
'When one door closes, another one opens.'
"There are people in the world who have it worse than you. Think of all the people starving around the world." Not only does this NOT make anyone feel better, it makes them feel GUILTY ... so now they feel worse about their problems.
"It could be worse." This just makes someone think about the OTHER horrible things that might happen.