Contextualise Your Budget : Of course your budget will be extremely important. But sometimes people sort of pluck figures out of thin air, not giving it the context it needs in the business plan to make real concrete sense of how that budget is going to work.
But do not be too paranoid, make sure you are showing it to people you trust, whose feedback you welcome and can be genuinely useful in guiding how the plan takes shape. Very often when working as individuals we get very close to certain details and miss out a big thing that has slipped your mind.
Remember the proverbial expression 'not seeing the wood for the trees'? You need to see the 'wood' first, then delve in and start examining the individual 'trees', meaning the individual items which you will be breaking down later. So a great point is to make sure that you have that overarching vision - and if you cannot find one, then maybe it is an indication that you are obsessing on a few technical aspects that do not necessarily make up a whole business as you had imagined it.
It could be, for example, the risk of a change in the economic environment - what are your contingency plans for that in terms of dealing with such a situation? There may be many other risks as well specific to your particular sphere of operation, but that ability to plan ahead for all scenarios makes for a robust business plan.