This in theory sounds like it makes sense but it is not always the case that giving in sometimes will produce unruly teenagers. Some posters on here clearly only have young children and lots of books on bringing up children. If you have older DC in their teens you get to realise that the theory on this stuff is often there just to make money and make parents feel insecure about intuitive parenting. Parents do get overwhelmed and with nights of endless broken sleep in the toddler years or just the general energy needed to keep them safe, you do just want tantrums or upset to stop and sometimes give in. I did because I wasn't a robot and my DC have turned out to be the kids that are considerate, well behaved and kind, they have friends who are similar. In the eldest's case they were the teenagers that achieved the highest GCSE grades in the school, the teachers love them, the English teacher wrote to me about how much of pleasure my DS has been to teach this was because she wrote to request that his already good grade get reviewed and the school pay for it as she thought he'd been robbed of a grade 9, we refused as didn't want to risk it. At parents' evening my youngest had nothing but praise, gets on with work no quibbles, gets homework in early. She often comes home to me and describes some 'popular' girls who don't stop moaning at the teacher, falling to sleep on their desk and she gets frustrated and DD wonders why they can't just get on with the work rather than complaining all the time. I know in two of these cases, the kids went to DD's primary school that the parents were the type to always assert their authority as the parent, often quite publicly, "no arguing with me I said no", forcing their uncooperative younger siblings in the buggy in the playground, que more loudness and battling, often they were their kids adversaries for the sake of it I think. I don't know there is something really miserable about all that I think, I becomes a game of who has the upper hand, but there appears no happiness with the children. Guess what, with both of my DC sometimes if they were upset and I wanted it to stop as it wasn't pleasant for them or everyone around them, I would just purchase a Thomas train with DS or a puzzle for DD or a comic and sometimes for example, I would make some boredom in a buggy better on holiday by buying them a soft toy or something from the gift shop as it is a lot to ask of a 2,3,4,5,6,7,8 year old to follow Grandma who dithered in cathedrals, palaces etc to enjoy the architecture and as she has bought DH up very strictly, she expected my DC to accept this just like she expected DH to when he was that age. It made life easier and I don't really care that it was 'giving in'. I didn't want to be my DC's adversary and I don't see that kind of upset as manipulation, that is ridiculous. I would often carry both of them if they were upset and push the buggy with the other hand. I think it is a corruption of your power as a parent to be so forceful and insistent on their upset.
On the other hand, I would say no but it wasn't a big deal, i.e "no, lets go down the slide now as another child is waiting". "No, we can't have that huge Lego toy today as we are here to buy food perhaps put it on a Christmas list (when they were older so 5/6)" crying rarely happened over such refusal. When they were very little I would distract and get out a toy I had brought from home. Obviously, upset did happen, DS went through a biting stage at 20 months, it lasted about 2 months but we just had to go home as obviously violence is not acceptable in any form.
Sometimes, in cafes not formal restaurants as silly place to go with a very young child, they didn't want to stay in the high chair, fine, I got them out and they sat on my lap. I don't understand why these power games are important to some parents, to win. My MIL was strict and would often look perplexed if I didn't for example force my child in to the buggy crying, she didn't understand why I would give them snacks to placate etc. I am talking an organix crisp but I don't think it has helped her relationship with her DC as my BIL is always falling out with her and they do talk about the formality of their childhood and my DC they find it easier as teenagers in particular to be with my Mum and sadly find Grandma a formidable person who is hard to be close with. I had a similar upbringing to my DC and again I was a well behaved, kind child and thoughtful teenager and I am close to my Mum.