“shakes hands.” The Hebrew is more literally something like, “striking hands,” but it refers to a custom that was either the same as our handshake or similar to it. The custom occurs here as well as in Proverbs 6:1 and 17:18. [For more on the custom of shaking hands, see commentary on Prov. 6:1].
“sense.” The Hebrew word is leb (#03820 לֵב), which is often translated “heart,” but this is one of those cases where that translation would cause confusion. In modern English, the word “heart” usually refers to emotion or passion, but that is not its meaning here. The function of the brain was unknown in biblical times, so things that we generally assign to the brain, like thinking, attitudes, understanding, and good sense, were assigned to the heart. In this context, leb, “heart” refers to the activity of the mind that includes good judgment, which is why we translated it “sense” (cp. BBE; CJB; HCSB; ESV; NAB; NASB; Rotherham; RSV).
People who make unwise agreements lack good sense. While it sometimes can be very hard to say “No,” to people who want help, an unwise agreement is still an unwise agreement even if it is difficult to decline getting involved. The wise person does not make unwise agreements, which is why this verse, and others like it, are in Proverbs (cp. Prov. 6:1-5). [For more on the Hebrew word leb and “heart,” see commentary on Prov. 15:21, “sense”].
“solemn pledge.” The Hebrew emphasizes the seriousness of the pledge by the figure of speech polyptoton. The Hebrew reads, “pledges a pledge.” The translation “solemn pledge” catches the sense of the text, and the emphasis of the Hebrew text could also be picked up by the translation that the person, “pledges, yes, pledges” in the presence of his neighbor (for more on polyptoton and the form of translation that uses “yes,” see commentary on Genesis 2:16).
Far too often people do not think through the agreements they make, or they get pressured into making agreements that they know are unwise or even one that they just do not feel good about making. Our natural human desire to please people and/or to avoid conflict often means we agree to things we really do not want to agree to. Wise believers draw inner strength from the Lord and do the right thing, including saying “No” to unwise decisions, even though they know some people will be upset by their actions.