秤砣虽小压千斤

1. • although small, a steelyard weight may tip a hundred pounds (idiom)
2. • apparently insignificant details can have a large impact
3. • for want of a nail the battle was lost

Character by character

• 秤(chèng)steelyard balance
• 砣(tuó)steelyard weight
• 虽(suī)although
• 小(xiǎo)small
• 压(yā)press
• 千(qiān)thousand
• 斤(jīn)catty