Always be kind, for everyone is fighting a hard battle. ~Plato
Geege Schuman stashed this in Compassion
I think it was Ian Maclaren, the pseudonym of John Watson, an English minister and writer .
Ronald, the Quote Investigator agrees with you:
Ian MacLaren was the pseudonym or pen name of Rev. John Watson. Wikipedia has an entry for MacLaren. His book “Beside the Bonnie Brier Bush” was a best seller in the 1890s. In 1965 in the Chicago Tribune the words attributed to Ian MacLaren are a close match to the quotation we are tracing [CTM]:
Most of us are acutely aware of our own struggles and we are preoccupied with our own problems. We sympathize with ourselves because we see our own difficulties so clearly. But Ian MacLaren noted wisely, “Let us be kind to one another, for most of us are fighting a hard battle.”
In 1957 a curious letter appears in Trenton Evening Times in New Jersey [TTM]:
Sir–A thought to help us through these difficult times: Be kind, for everyone you meet is fighting a hard battle.
This provides more evidence that the quote of interest is associated with Ian MacLaren. But the Scottish author died in 1907, and so the writer who signed the letter with his name was perhaps reusing the old pseudonym. In 1947 the saying appears in a Charleston, South Carolina newspaper [SCM]:
Not until trouble and heartache and sorrow came into my own life could I fully comprehend the words of Ian McLaren: “Let us be kind, one to another, for most of us are fighting a hard battle.”