Both Uses

intrusion
in
The Shack
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Or the intrusion of your soul's sickness that inhibits and binds you, or the social influences around you, or the habits that have created synaptic bonds and pathways in your brain.†
Chpt 6.

intrusion = an interruption or involvement that is unwelcome
Although Mack felt like he was intruding, no one else seemed concerned and he really had no idea where he would have gone in any case.†
Chpt 7. *

intruding = interrupting or involving oneself without welcome

Definitions:

(1) (intrusion)
an involvement or interruption that is unwelcome
(2) (meaning too rare to warrant focus)
In geology, intrusion can reference the forcing of molten rock into fissures or between strata of an earlier rock formation.