social dynamics

A small favor makes a large request more likely.

A 1966 study found that people who agreed to a trivial request were significantly more likely to agree to a larger, related request a few days later.

The original study conducted by Freedman and Fraser utilized a timeframe of a few days, not two weeks.

Once you agree to a small initial term, your identity begins to shift to accommodate the commitment.

Where this comes from

Study: Freedman and Fraser, 1966, Journal of Personality and Social Psychology
What the check found: The study occurred, but the timeframe is misstated as two weeks rather than a few days. The attribution to Freedman and Fraser (1966) is otherwise correct.
Confidence: Solid, with limits

One of these every day, and every one names the study it came from. When a finding is contested, it says so.