If you want a big company example look at what Burger King did to McDonalds in the late-70s/early-80s, BK decided to position themself in the adult burger market and move away from the childrens market. BK stopped running adverts during childrens tv.
McD's own adverts carried on running in between kids shows, the context of the ads (in contrast to those of BK) caused McD to seem like a childen's brand. This allowed BK to steal a massive chunk of McD's market share.
McD's own advert harmed the McD brand purely because of context.
While there were clearly other factors at play here, the context in which those adverts ran was a major contributing factor. You could see how the same could apply today with regards to adverts appearing on children's websites, etc.
McD's own adverts carried on running in between kids shows, the context of the ads (in contrast to those of BK) caused McD to seem like a childen's brand. This allowed BK to steal a massive chunk of McD's market share.
McD's own advert harmed the McD brand purely because of context.
While there were clearly other factors at play here, the context in which those adverts ran was a major contributing factor. You could see how the same could apply today with regards to adverts appearing on children's websites, etc.