effort

You value things more just because you suffered for them.

Effort justification is a specific paradigm derived from cognitive dissonance theory, most notably demonstrated by Aronson and Mills in 1959.

Aronson and Mills (1959)

You love your struggles more than the rewards they bring.

Where this comes from

Study: Festinger, 1957
What the check found: The definition is correct, but the citation is imprecise; Festinger's 1957 work provides the theoretical foundation, while the specific effort justification paradigm is from Aronson and Mills (1959).
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.