There is nothing more dreadful than the habit of doubt. Doubt separates people. It is a poison that disintegrates friendships and breaks up pleasant relations. It is a thorn that irritates and hurts; it is a sword that kills.

This quote states that doubt has a negative effect on relationships. It can make us feel like we are alone and isolated from others. Doubt can also damage friendships and create arguments and discord between people. It can cause pain and hurt, and can divide and destroy relationships. In other words, doubt can be destructive and can have a detrimental effect on our relationships.