Electronics drift outside their characterized range. Battery capacity falls off. Elastomers cycle past their service window. Combined thermal-vibrational loading attacks every interface in the string. The failure modes stop being theoretical, they show up in the run report.

Octane XT MWD field data:

→ 219 runs sustained above 320°F
→ 96.3% success rate

That's a defensible sample size, in the operating envelope where most tools start trending toward derated performance. Engineered for thermal margin, not just nameplate temperature.