You have been influenced when you think something you wouldn't otherwise have thought, or do something you wouldn't otherwise have done.
In the 20th Century, the marketing department did marketing, the PR people did PR, and no job title included the word influence. To this day, no role or team or department in the typical organization incorporates the word, which is why I pivot my client workshops around the topic of influencing and being influenced – not only does it address the actual thing we're all interested in, it helps lower ego defence and removes functional blinkers.
Only very recently are organisations looking up from the typically too-narrow focus of PR, which for some reason appears to have restricted itself to media and analyst relations of recent times, and looking away from the pay-to-spray-and-pray domain traditionally occupied by the bods in advertising, to investigate the effectiveness of so-called influencer marketing.
While this is just a sub-domain itself of the deeper and wider influence system, I thought, given this trend, you might find the following 30 seconds of video interesting. It documents the efforts Adobe Systems went to towards the end of the 1980s to get its Illustrator software accepted.
We called it influencing the influencers.