A proverb meaning 'you won't know until you try' or 'it's worth trying'; encouraging someone to give something a go.
新しいレストラン、物は試しに行ってみよう。
Let's try the new restaurant — you won't know until you try.
物は試しだから、ダメ元で応募してみたら通った。
Since it's worth trying, I applied with nothing to lose — and I got accepted.
そのスマホ、物は試しで一週間使って判断しよう。
Let's try that smartphone for a week and then decide.