Why do opponents of a bill have an advantage over supporters of a bill in the legislative process?

1: Why do opponents of a bill have an advantage over supporters of a bill in the legislative process? 2: How does this advantage affect the proportion of bills that become law? 3: How does the “traditional” filibuster differ from the modern use of the filibuster? 4: What factors motivate Members of Congress to seek a specific committee assignment? 5: How can a member of Congress use their committee membership to help win reelection? Provide an example (real or hypothetical).