first off, i want to say that i think as parents we need to realize that though our children are young, they are not unreasonable. while children's reasoning capacity may not be matured, i do believe they are capable of being reasoned with.
i have an extremely reasonable 2.5 yr old and an even somewhat reasonable 3 month old (if you can believe that, but i do!). for example, my 2 yr old like so many other toddlers used to hate going to bed. when he does want to go to bed, he wanted daddy or mommy to sleep with him the whole night and cried the minute we get up and leave the room. after a few nights of this, my husband and i realized we couldnt keep staying in his room for hours until he finally fell sound asleep.
one night, we did our same bedtime routine of teeth brushing, potty, and bedtime story. but once the story ended, i carefully explained that i couldnt stay in his room the whole night and that i had to go do chores like wash the dishes. of course, he did his cry that he usually does but i gave him options. i told him i could either leave and close the door and turn the nightlight off or i could leave and keep the door open and keep his nightlight on. i told him that if he ever got worries about anything, call me, and i will come and check on him to make sure he was fine. he stopped crying, thought about it, and said he wanted the door open and night light on.
i left the room and maybe 5 mins later, he would call me. i came, asked him if he was ok, which he said he was and i said good night. 10 mins later he would call me again and i would come, ask him if he was ok and leave. i came quickly every time he called me bc i wanted to reassure him that even tho i wasnt in the same room with him, doesnt mean i've forgotten about him. we did this for the next 3 nights and by the 4th night, when we did all the bedtime routines, he said good night and immediately fell asleep. it is such a relief!
my son goes through his share of tantrums, but i'm also the kind of parent that is not embarrassed by those tantrums when they happen in public. he's rolled in the floor crying and screaming in the store or at the park for whatever reason. i stand there every time and tell him that i would stand there until he was done crying but i wont know what to do unless he tells me what's wrong. if he refuses to budge, i tell him, ok you can stay here by yourself or you can come with me and we can go explore different things in the store. of course, i would never leave him but it works every time. he doesnt want to be left behind :)
if we're at home and he's being extremely difficult, i tell him, ok we need a break. i want you to go to your room and sit on your bed and think about why you are being bad right now. i'm going to keep the door closed so you can think quietly. usually, he cries and cries when i do this, but 1 of 2 things always happens. he either falls asleep immediately or he cries and 5 mins later i come and he'll immediately say, "i'll be nice now mama. can i come out now?" and i let him out and it's as if order returns to the household :)
as far as my 3 month old and reasoning with him, i talk to him all the time. with both kids, every single thing i do, i explain to them regardless of whether they understand what i'm saying or not. my 3 month old only cried with diaper changes the first month. every time i change his diaper, i explain to him i'm changing it bc he's got a messy diaper and that he'll feel so much better once i put a new one on. i do this every single time and i say the same thing every single time. repetition is key! now my 3 month old knows that he is getting his diaper change and keeps his eyes on my mouth when i change him and even coos back to me. there's no struggling or crying and it's such a pleasant experience.
ok, i'll end it here, but i hope this helps you somewhat. good luck!