Granny Smith has seen and felt more than a lot of ponies could ever understand. She takes all of this pain and responsibility upon her back because she wants nobody to ever feel what she feels. With Big Mac being the way he is in the show - quiet, hard-working, and wise - I’d say he and Granny had an important heart-to-heart about biting off more than one could chew.
 
I see young Mac trying to do everything his parents did, because he felt it was the right thing to do and needed of him. I imagine he ran himself ragged until Granny Smith took him aside and assured him he had nothing to prove, and that he wasn’t expected to shoulder the burden he had taken upon himself. Granny Smith made herself the head of the family unit so that the children - especially Mac - could still have a childhood. This is likely why Granny Smith remains the clan leader to the present day, and not retired and being taken care of by her grandchildren. She wants to guide them on a path that keeps them all close and happy, and steers the young’uns away from the majority of the pain and stress of losing ponies they loved so much.
 
Granny will always be cranky at times. Heck, if the show didn’t have a general rating, I’d bet she’d swear a lot when angered - but will ground anypony she catches swearing. When you’re as old as her and seen enough of the world, only then can somepony go into a cursing fit from time to time!

@Background Pony #4551  
EVEN IF SHE HAS TO MAKE IT HAPPEN.

@Background Pony #4551  
Doesn’t mean it isn’t going to impact him though.

@ZhaoZoharEX  
Knowing granny Smith she is only gonna die when Mac finds a good girl to take care of him.

Now that I think about it, I wonder how hard it would hit Big Macintosh when Granny Smith eventually passes away. Oldest child with no living parents and only his grandmother and two sisters… I think a part of my heart just died. :(

@Azulgatos
 
@Kolbjorn
 
The feels have been doubled…

@Kolbjorn  
Damn… I have more respect for Mac now.

I always tought that Big Mac got it really hard. he was a young colt with a loving family and suddenly he lost his parents and became the stallion of the house, work even harder on the farm to help granny smith and take care of his younger sisters. Maybe thats why he really wanted the smarty pants doll, a little bit of his foalhood back

“Why did Ma and Pop go away?”