Many have analysed life of Mahatma Gandhi and volumes are written about him.
In my view, his foundational truths came in two phases.
First, when he was a child of about 4 to 5 years, when he saw a stage drama of story of King Hsrishchandra.
Second foundational truth came in college days when he came in touch with meanings of about 20 stanza of GITA
Story of King Harishandra is about a King who had taken vow to speak nothing and nothing but the whole truth. His vow puts him into troubles. He loses Kingdom. He and his family are sold as slaves. And yet he refuses to break his vow. In the end, the God becomes pleased with him and he emerges victorious and his Kingdom and family are restored.
Second foundational truth came when he understood about 20 Stanza of GITA during his college days.
Everyday, he recited and memorised these stanza from GITA.
The stanza mainly said
1) You are a soul. The soul is immortal. Births and deaths are like changing clothes for the soul. No weapon can kill the soul.
2) You have no right to claim outcome or reward of your action. Outcome of every action is result of inputs from several factors. You cannot claim sole ownership of outcome of your work.
Your job is to do your duty, you never have any rights on fruits of your action. The fruits of your actions belong to Eternity.
His life was centred around these two foundational truths.