Date: 20 Adar Rishon 5565
From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer establishes that when a person had an opportunity to fulfill an obligation but was lazy, any subsequent unavoidable circumstance (ones) — including forgetting — does not exempt him, because his situation began with negligence (techilaso b'peshia). He defends the Agudah's derivation of this principle from the Mishnah in Arachin regarding batei arei chomah, resolving Tosfos's question about why buyers bothered to hide and dismissing the Taz's objection. The ruling applies broadly to oaths, prayer, and property redemption.
Source: Shu"t Chasam Sofer CM §42