Whoah -- heart means heart, unless you are accepting extending meanings that are understood by a translator and inserted in the English. When "mind" is added, it changes the meaning. Why is "mind" ok to insert but not "own"?
Own is mine, not your. I think that heart is always metaphorical and means what a person will do.
I think that lean means to let a belief cause behavior. The governing body of Jehovah's Witnesses came with the belief that they are being used by God to be correcting the attitudes of the faithful of God.
They really believe that they are personally chosen to lead the people safely out of the great tribulation.
If that is true, then it can be said that they are leaning on Christ's understanding. They wouldn't be disrespecting Proverbs 3:5 because the understanding is not their own. It seems to them to be coming from God.
It wasn't hard for me to understand that they were teaching some scriptures wrong. It had not occurred to me that they were teaching Proverbs 3:5 wrong while I was with them. I was with them with my time, my effort and my money for almost twenty years because I would not lean on my own understanding. I also know it is not humanly possible to see inside their hearts to know they are leaning on their own understanding. I realize that now, but it takes awhile.
If Proverbs was copied without the added meaning, as soon as I realized that Jesus is not the one pictured at Revelation 6;2 I might have left them then and saved myself a lot of grief and a little money.
The reason why is because I would have known that by their teaching something that I knew was wrong they were disregarding the important rule at Proverbs 3:5. They are telling us to obey them, but they do not obey what is written by God as they believe all scripture is of God.
Some people can't see the difference between Proverbs the way it is and Proverbs the way I think it was. I can.