Dave's (as usual) excellent and informative post communicates the necessity of thinking quickly and being flexible in the creative world in which we live.
However, another important point that Dave doesn't mention is the importance of collaboration. While John Lloyd may have produced Blackadder, he didn't create the show. Rather, he was part of a team which created a whole greater than the sum of its parts.
In fact he wouldn't have got to the stage where he could produce Blackadder had he not worked on Not The Nine O’Clock News. Which he probably wouldn't have worked on had he not worked on Hitchhiker's Guide, etc.
By working on these other creative projects, he met people who he could bounce ideas off, who stimulated him and inspired him.
The point is that what we do now is a domino effect in regards to our future. If as a junior team we can get in to a large creative agency now (with the chance to meet many other top creatives), it will multiply our chances of being creative and successful further down the line.
Which is why "cashing the check" right now is more important than ever.