Reproduction means obtaining the paper's reported numbers yourself.
It is the single best way to learn a method properly.
Reading gives you the idea, and building it shows you what the idea requires.
Start from the official code release if one exists.
Expect gaps, since papers routinely omit details that turn out to matter.
Learning rate schedules, initialisation, data preprocessing and seed selection are the usual omissions.
Match the environment as closely as you can, since library versions change behaviour.
Start by reproducing on a smaller scale before committing real compute.
Get a small model to overfit a tiny dataset first, which proves the pipeline works.
Compare intermediate values against the reference rather than only the final metric.
Being close but not equal usually means a preprocessing difference.
Failing to reproduce is a genuine finding and worth reporting.
Many published results are fragile, and some do not survive careful re-examination.
Check whether the gain survives a fair baseline and several random seeds.
A result that holds only on one seed is noise with a paper attached.