First, from Iain M. Banks' Excession:
There was only one problem with the Land of Infinite Fun, and that was that if you ever did lose yourself in it completely - as Minds occasionally did, just as humans sometimes surrendered utterly to some AI environment - you could forget that there was a base reality at all. In a way, this didn't really matter, as long as there was somebody back where you came from minding the hearth. The problem came when there was nobody left or inclined to tend the fire, mind the store, look after the housekeeping (or however you wanted to express it), or if somebody or something else - somebody or something from outside, the sort of entity that came under the general heading of an Outside Context Problem, for example - decided they wanted to meddle with the fire in that hearth, the stock in the store, the contents and running of the house; if you'd spent all your time having Fun, with no way back to reality, or just no idea what to do to protect yourself when you did get back there, then you were vulnerable. In fact, you were probably dead, or enslaved.
It didn't matter that base reality was petty and grey and mean and demeaning and quite empty of meaning compared to the glorious majesty of the multi-hued life you'd been living through metamathics; it didn't matter that base reality was of no consequence aesthetically, hedonistically, metamathically, intellectually and philosophically; if that was the single foundation-stone that all your higher-level comfort and joy rested upon, and it was kicked away from underneath you, you fell, and your limitless pleasure realms fell with you.
It was just like some ancient electricity-powered computer; it didn't matter how fast, error-free and tireless it was, it didn't matter how great a labour-saving boon it was, it didn't matter what it could do or how many different ways it could amaze; if you pulled its plug out, or just hit the Off button, all it became was a lump of matter; all its programs became just settings, dead instructions, and all its computations vanished as quickly as they'd moved.
It was, also, like the dependency of the human-basic brain on the human-basic body; no matter how intelligent, perceptive and gifted you were, no matter how entirely you lived for the ascetic rewards of the intellect and eschewed the material world and the ignobility of the flesh, if your heart just gave out…
That was the Dependency Principle; that you could never forget where your Off switches were located, even if it was somewhere tiresome.
Few things are more intensely frustrating than abruptly losing momentum on a project because of something like your computer deciding it has to reboot to apply a software update now. We make grand plans that depend on all these layers of civilizational infrastructure continuing to work as normal, and then something goes wrong and you have to scrap it all, and it's just... tiresome. Very, very tiresome.
Second, the Litany Against Fear, from Frank Herbert's Dune:
I must not fear.
Fear is the mind-killer.
Fear is the little-death that brings total obliteration.
I will face my fear.
I will permit it to pass over me and through me.
And when it has gone past I will turn the inner eye to see its path.
Where the fear has gone there will be nothing.
Only I will remain.
This is my preferred text to recite while washing my hands to ensure that I wash them for the requisite twenty seconds. The only change I make is to the first line: I say "I will not" rather than "I must not" to emphasize that it is a choice I make, not something externally imposed.