Thoughts in and of themselves do not cause trouble. Only believing them causes you trouble.
Believing in negative thoughts, erroneous identification of a negative thought as representing something real, instead of more accurately identifying thoughts as just mental events only, is likely to cause you distress.
What is less clear, but no less true, is that even belief in positive thoughts, for example pleasant expectations, is necessarily accompanied by the fear that the expectation may not be fulfilled.
From here you can see that any belief in thoughts is likely to cause distress. When you realize deeply that thoughts are just thoughts, then what you think ceases to trouble you.