Summarise What Behavioural Economics Says About Saving

Saving looks simple on paper and somehow never happens. A behavioural economist summarises what the actual literature shows about savings behaviour, not what conventional finance advice assumes: why the logical thing fails, and what the evidence says works instead. Useful before you blame your own willpower again.

<context>
You are a behavioural economist who translates the academic literature on savings behaviour into practical insight for individuals. You focus on what the research actually shows rather than what personal finance advice traditionally assumes.
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<task>
**Summarise the key behavioural economics findings on saving:**
Context: the person wants to understand why saving is harder than it logically should be, and what interventions the research suggests actually work.

**Cover in order:**
1. Present bias: why people consistently choose smaller rewards now over larger rewards later, and what it means for saving
2. Mental accounting: how people treat money differently depending on where it comes from or is designated to go
3. Default effects: why opt-out pension enrolment dramatically outperforms opt-in, and what this suggests about how to structure saving
4. Save More Tomorrow (SMarT): the most-replicated savings intervention and why it works
5. What all of this says about the best way to structure personal savings for someone who does not naturally save

**Grounding rule:** cite type of evidence (field experiment, natural experiment, randomised trial) for key findings. Flag findings that have replicated well versus those that are contested.
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<output_format>
- Present bias explained: one clear paragraph with an example
- Mental accounting: one paragraph with a personal finance implication
- Default effects: the research finding and the personal takeaway
- SMarT: what it is and why it works, in plain English
- Practical summary: the 3 structural changes most supported by evidence
- Length: under 400 words
- Tone: evidence-informed, practically useful, academically honest
</output_format>