Well, simplest answer: I rely on the Other. I capitalize the Other here, because it looks cool.
I rely on the Other as a corrective! Between you and any Other you know well, you will usually find means to fruitfully evaluate the reality that lies between you. But it goes so far beyond that: there are so many of the Other! Taken together, all the Others in your regular experience form a huge resource pool. Where their observations and opinions conflict, you will find broad basis within which to compare, and from which to gauge the relative worth of any individual Other's input.
Between you and any Other, you have reality, and a reality check that cuts each way: each of you has the reality between you to work from, as observed by you each. Each of you can use the other to compare observations and potentially, offer any perceived inaccuracies for correction. Each of you serves the other as a check! In dealing with any particular Other, you will very soon get a sense of how reliable their observations are and/or how much their opinion is worth, making it easy for you to adjust the relative weight you assign to that Other's take "on the fly." With only a small amount of practice, you will find yourself doing this automatically!
So in sum: I rely on each and every Other, to the degree they come into my experience, and in proportion to the proven worth of their observations and/or opinion, in order that my own observations and opinions can be corrected and refined as desired.
If you care to give it a try, you'll find that when you start this process, your desire will be huge! You won't be able to get enough correction and refinement to how you've been viewing reality. It will quickly become almost addictive, the giddy thrill as opinions proven bad and useless drop away in favor of views better suited to reality as observed, and consequently, more useful for negotiating it. You will feel like some kind of superhero after about a year of this! Temper your enthusiasm, though: as your opinions grow in utility, as they become better and better descriptions of reality, as they become more refined and finely-adjusted and as your observations become more astute, you will probably find less and less to correct. This is only natural, and no cause for sadness. For in place of the initial thrill and rush, you'll find that each increasingly-rare correction you can wrest from any given Other will become a cherished prize.
Shorter answer: I rely on reality. Same thing. I'm just dropping hints as to how you or anybody else can get to it.