Overcoming issues (making changes on the fly)

I'll use me as an example.  This last week I caught a very nasty bug.  So for the last 8-10 days I've been unable to eat properly, lost weight, felt weak & been unable to train.  I think this is certainly the worst illness I've had in well over a decade (maybe 20 years since I was anywhere near this bad!), so I realise my immediate training plans are up in smoke as I have to think about regaining previous mass, so when I get back to training the plan I had has just been chucked out the window & it will be a hypertrophy (muscle growth) phase. 
Stuff like this happens, it can be illness, injury, sudden change in circumstances.  It can be a pain if you planned a cycle or two where you wanted to make some real strength gains on your 1 rep max & instead you have to spend time building up the size again as you've lost a lot unexpectedly.  Those are the breaks when it comes to training in the real world, stuff happens!

If you are a beginner this won't affect you too much as you just get back on doing a weight you can do & begin the build up again, but as you develop a goal, you have to play about with things as you work towards it.  For me I know I need a certain bodyweight to perform or I suck in terms of strength, so although my goal is to achieve a decent amount of absolute strength, to achieve that I need to build up my size a bit more again, that is the only option for met.  For some people that might not be an issue.  You may need find that after a stressful month you've added fat & so need to move from a mass building to a cutting phase for example.  Sometimes we need to adapt when life smacks us in the face.  So, don't be afraid to change the plan if you have to.  This isn't an excuse to have you swapping up stuff every few days as you find THE new routine in "Big & Buff" magazine (trust me it's not 'THE' routine, it's just a routine often written by the copy writer for the magazine & then they add the pictures of the latest Mr Perfect to that - Mr Perfect does his own routine & has 'supplements' to help him achieve his results).
So, plan your training, but remain flexible enough so that when the world hits you in the face you bounce & don't splat!
If you've hit a roadblock in your training, don't hesitate to post below, or for a more indepth answer pop over to the messageboard at http://veganbodybuilding.userboard.net/ & get the help of a whole herd of clever people!