"It was a good self-investment."
"it was ~" 「〜だった」
"a good ~" 「良い〜」
"self-investment" 「自己投資」
"It was a good investment for my work."
"it was a good investment" 「良い投資だった」
"for my work" 「私の仕事のために」
"I made a good investment for myself."
"I made a good investment" 「良い投資した」
"I made an investment" 「投資をした」
"for myself" 「自分のため」