In my everyday life I've found that I can be very oblivious to my surroundings if I'm with someone else who I feel "safe" with. I'm not sure that the person or gender of that person matter as much as the fact that if you are traveling in a group I guess it feels like you are less likely to be approached by others, whether friendly or not, and I feel I can let my guard down a little bit. I don't particularly mind being alone to travel and do things like ski, but I prefer meeting up with others at some point along the way. I'll go solo if I want to go somewhere and there isn't anyone else available to accompany me though. I'm not really into people approaching me that are strangers, so I feel like prolonged solo travel would get too lonely for me. I'm okay with say striking up a conversation with people near me in a bar or something if I'm eating dinner alone, though I'll often pull out my kindle in that situation because I prefer that to random chit chat with a stranger. I'm not the best at small talk in general so I don't always find I have the energy to want to deal with it with someone I'm never going to see again anyway, though sometimes things just click and it's so worth it and a great experience. I've also had too many experiences where those people (male) that start out really friendly and nice don't know when to go away and decide they should pursue more than conversation, so I'm always wary of strangers if I'm traveling alone for work etc.
If I am alone even just walking the dog or in a parking lot etc. I am very aware of my surroundings and do some of the things others have described like checking around cars in the parking lot. This especially started after reading a true crime book on Ted Bundy that really creeps me out to this day. My father definitely drilled this stuff into my head my entire life, seemingly a bit like
@bounceswoosh 's description of her relationship with her mom. I usually carry mace with me, (it's a thin metal tube variety on a keychain and kind of looks like a thin flashlight, so if you don't know what it is you wouldn't know just from seeing it, but it shoots a powerful amount of spray up to around 5-6 feet away very accurately) and this gives me some sense of security, whether it should or not is up for debate since I've never had to try defending myself with it beyond practicing with a dummy canister in case I ever really needed it. I normally have it in my purse in general, but if I'm walking to my car somewhere sketchy late at night or somewhere I feel uncomfortable then I'll have it in my hand at the ready or at least in my pocket where it's very easily accessible because digging around your purse by the time you might realize it's needed isn't going to cut it in my opinion. The trick is also making sure to leave the mace in the car or wherever if you are attending an event where it isn't allowed inside if your purse is being searched. I'm always super paranoid that I'm going to forget sometime and try and go through security at an airport or something, so I try to remember to leave it at home a good week ahead of that type of travel where it isn't allowed. I used to carry a knife, but then I realized how close someone would have to be to make that a weapon of choice and how I have absolutely no experience defending myself in that manner and could easily be overpowered into an even worse position so mace seemed like the best option for a little peace of mind.
As an aside, mace is what was recommended to me by a state trooper as the best weapon of self defense for both men and women. Even if you carry a firearm, he recommended mace as a first attempt at keeping someone at a distance who was being menacing as it usually stops someone in their tracks and you can hopefully get to safety. The only scenario where mace may not be effective is if someone is very high on drugs where they aren't registering the pain, but hopefully you can spray, cause some distraction, and run still. The mace also usually colors the persons face and hands when they go to cover their face, so it can be good to identify the perpetrator if they are able to locate them in the area soon after the incident.