Speaking at the inaugural JCDecaux Creative Forum lecture in Dublin, Beattie told the audience: "Life's too short to be mediocre."
Appropriately enough for a lecture hosted by an outdoor media company, Beattie said that outdoor poster advertising was his favourite medium, saying that there was no hiding place when it came to posters and that, unlike television ads, you can not produce a great soundtrack to cover up a mediocre poster.
Beattie is most famous for his "Hello Boys" poster for Wonderbra and for bringing FCUK to prominence through poster advertising, which has featured the likes of Lennox Lewis.
The TBWA\London chairman and creative director also said that branding was one of the most misunderstood words in marketing, saying that brands are too often confused with logos.
"It is impossible to increase branding by 100% but it is certainly possible to improve it by 100%," Beattie said.
Niamh Cleary, managing director of JCDecaux Ireland, said: "Trevor made it clear that posters work best when those behind the campaign are also aware of the environment in which the poster is being viewed.
"This couldn't be more true. Advertisers and creatives must realise all the aspects of outdoor -- not just design -- to fully exploit its power as a mass medium."
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .