TT #306 · Parashas Shoftim · Seventh Aliyah · Passuk 20:08
And the officers shall continue to speak to the people and say: Who is the man who is fearful and faint-hearted? Let him go and return to his house, so that he not melt the heart of his brothers as his own heart.
Torah Temimah points to Sotah 44a.
TT lemma: וְלֹא יִמַּס אֶת לְבַב אֶחָיו כִּלְבָבוֹ.
English: ‘So that he not melt the heart of his brothers as his own heart’ – for fear is contagious.
Derash on the contagion of fear (Bavli) — one fearful man endangers the spirit of the unit.
Fear spreads; therefore the Torah removes the fearful man so that he does not demoralize his comrades.