Why Does My Neighbor Borrow Things He Never Returns?
Possession rewrites how a person feels about an object faster than any agreement they made about it. Your tools stay over there because of: 1) the endowment effect, once it sits in his garage it starts registering as his 2) mere ownership bias, where he begins remembering it as a loan that never had an end date attached 3) social cost asymmetry, because asking for it back costs you a neighbor and keeping it costs him absolutely nothing. Lend with a date attached or do not call it lending.
Why this keeps happening
His garage changes the ownership
The loan loses its end date
Asking costs you, not him
Lend with a return date
How it escalates
Ask for it back on a Tuesday and see which of you gets uncomfortable.