Given the following declarative pipeline:

pipeline {
  stages {
    stage('Example stage') {
      when { expression { false } }
      options { lock resource: 'example resource' }
      steps { // ... }
    }
  }
}

Even though 'example stage' is skipped due to the when conditional, a lockable resource 'example resource' is created (if it doesn't already exist) and a lock is acquired on it. I think this is counter intuitive. The consequence is also really bad – a skipped stage might actually make the whole build hang (possibly for a long time) because it needs to acquire a lock on a busy resource (typically used by another build).