Vitaliy M. wrote:I do not see why one would overestimate what they could and cannot do by a mile (it puts both people in danger).
I can name a couple of reasons since I've been out with many new or untested partners and am used to attempting to screen them for their adequacy as partners:
1. They have poor self-assessment. e.g. when I request partners for a route with x-thousand feet of gain and y-miles (scrambling or approach), I've had many people express interest in the climb who had never done x-thousand feet of gain or y-miles in a day, but they considered themselves fit and assumed they could do it. When I tell people about a route, I never assume their interest in attempting it means that they have a realistic concept of what the details of the route really mean. I ask them things like how many feet or how many miles they've done in a day and how easy was it, highest altitude reached and how they felt (for higher altitude peaks), their perceived hardest day out and why (quite revealing and gets across things not shown by numbers). Similar thing with technical details. I don't assume a 5.11 leader can handle a 5.9 chimney or OW, or that they'd be comfortable simul-climbing. Of course you can't know everything from questions, but I think it is good to anticipate for a given route what is really critical and probe deeper on those details.
2. They have poor risk assessmentThey see climbing as similar to any other sport, not fully appreciating the risks, and expect it to be fine for you to pick up the slack if/when they become inadequate partners. Similar thing to watch out for when taking a sport climber on a trad climb, cragger on an alpine climb, etc. on their conservatism on their self-assessments and self-reliance when entering increasingly less predictable and more dangerous terrain.
I've had a few bad cases of partners in this category. I'd say their core problem is that they don't fully appreciate the potential danger of these climbs and what can go wrong if they get in over their heads. In fact one of the worst cases was with a guy who I climbed with based ONLY on personal references from a climber friend and some general resume stuff like 'climbs 5.xx on sport, boulders Vx, has been leading trad for a year and is just starting to do some alpine climbs & looking for more alpine experience'. That was a mistake

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I watch closely to see how well people match up to their claims of adequacy in both of these areas- some people underestimate themselves and some overestimate themselves. Getting that sense of a partner helps me determine how to view them in the future as partners in terms of adjusting my expectations of their strengths, abilities, judgment, and blind spots. It is also enlightening to pay attention to how they cast themselves in the future when they fail to meet expectations (bad day out, innocent mistake, or blatantly misleading or dismissive?).