The verses contain only major chords:
G major | D major | G major|: C major | G major :|G major | D major | G major
while the bridges consist mostly of minor chords:
|: E minor | B minor :||: A minor | D major :||: E minor | B minor :|A minor | B minor | C major | D major
The perceived sadness of minor chords matches the sentiments in the lyrics in the bridge ("When you get so down that you can't get up" and "When you're so down-hearted and misunderstood"), especially when contrasted with the major chords and the more hopeful encouragement in the verses (the repeated "Hold on tight to your dream").
